It rains quite a bit in january,february and to some extent in march in Mauritius due to the cyclone season and the development of low pressure areas in the south west basin of the indian ocean....... This however affects more the central plateau ( the higher grounds ) and the east coast, it actually does rain less on the west coast. If you do go to Mon Choisy, you should get some decent weather with only a few days of rain as it is situated on the west coast of the island. I do go to the island every year for my hols but in october when the weather is at it's best with minimal rain and agreeable temperatures at night.
I wish you a nice holiday in wonderful Mauritius,